Changes of soil and plant tissue selenium status in an upland grassland contaminated by selenium-rich agricultural drainage sediment after ten years transformed from a wetland habitat.

A field survey was conducted in 1989, 1994, and 1999 in order to monitor the soil and vegetation Se concentrations at the Kesterson upland grassland contaminated by Se-rich drainage sediment. The rate of Se dissipation estimated by the change of soil Se concentration, via volatilization, found to be about 1.1% per year. Soil water-extractable Se increased in 1994, but greatly reduced in 1999. The increase of soil Se concentration in the top 15 cm of soil at the fresh-soil fill sites indicates that the plants were able to effectively take up the soluble soil Se from the lower soil profile and to deposit it on the top of the field. This process may reduce the rate of leaching of soil Se. Overall, the concentration of soil water-soluble Se was relatively low and it is unlikely that problems of transport of Se from the Kesterson soil to the adjacent uncontaminated environment by leaching can occur. Plant tissue Se concentration was found to coincide with the soil water-extractable Se concentration. The average plant tissue Se concentration and soil water-extractable Se detected in 1999 was about 10 microg Se g(-1) and 110 microg Se kg(-1) dry weight, respectively, and the estimated bioaccumulation value of this upland grassland is less than 10% of the previous wetland habitat. Therefore, the existing Kesterson grassland should not be at high risk to the environment.